The present invention relates generally to a heatsink which is used to cool heat producing elements such as integrated circuits (IC), central processing units (CPU), micro processing units (MPU) and other semiconductors and electronic components with heating sections. The present invention also relates to methods of manufacturing the heatsink, and to cooling apparatus using the heatsink combined with a cooling means such as a fan for cooling the heat producing elements.
Integration of electronic components such as semiconductors and increasing frequency of operation clocks have been raising the heat produced by such components in recent years. Under such circumstances, maintaining temperatures at contact points of the electronic components within the operation temperature range has become a critical issue for the normal functioning of the electronic components. Increases in integration and frequency of the micro processing units (MPU) has been remarkable. Thus, dissipation of the heat produced by MPUs is particularly important for stabilizing their function and securing their operational longevity.
In general, heat produced by various electronic devices is dissipated by a heatsink which expands the heat dissipation area and effectively transfers heat to a refrigerant such as an air, and a cooling apparatus comprising a fan with a motor which forcibly blows air into the heatsink.
Heatsinks of the prior art are described below with accompanying FIGS. 14, 15 and 16.
FIG. 14 shows a perspective view of a construction of a conventional heatsink, FIG. 15, plan and side views of a construction of a conventional cooling apparatus, and FIG. 16, perspective and side views of a construction of another conventional heatsink.
These heatsinks can roughly be categorized into the following three types; a plate-type heatsink where a plurality of plate fins 1a made of many thin plates are disposed on a base plate 2b or a heat conduction section as shown in FIG. 14(a) ; a pin-type heatsink where many pin-type fins 1 are disposed on the plate 2b as shown in FIG. 14(b), and a tower-type heatsink where a plurality of plate fins 1c made of thin plates are disposed vertically to the axis of column 2 as shown in FIG. 16(a). These heatsinks are mainly constructed of materials with high heat conductivity such as aluminum and copper, and produced by the extrusion molding (otherwise called pultrusion molding) method, the cold forging method, the die casting method, or the thin plates accumulating method.
In the case of the pin-type heatsink, the heatsink is mounted either directly onto a heat producing element 3 as illustrated in FIG. 15(a), or indirectly by inserting a heat diffusion plate 2c between the heat producing element 3 and the heatsink to transfer the heat produced by the heat producing element 3 to the heatsink and to dissipate heat, and to protect the heat producing element, as illustrated in FIG. 15(b).
The cooling mechanism of the cooling apparatus in use, is described as follows: heat produced by the heat producing element 3 as shown in FIG. 15(b), is conducted to the pin-type fins 1 via the heat-conductive base plate 2b made of a highly heat conductive material such as aluminum, and, over the surface of the pin-type fins 1, convectively conducted to the air blown by a cooling fan 4 thus dissipated into the air and cooled. In order to improve the capacity of the cooling apparatus, heat is most desirably distributed throughout the heat conductive section evenly, and dissipated from all of the dissipation fins. However, in the case of the plate-type and pin-type heatsinks, heat emitted from the heat producing element tends to be conducted intensively to the heat dissipation fins disposed right above the heat producing element. It is relatively hard for the heat to be conducted to the peripheral heat dissipation fins. The reason for this is that the heat producing element is much smaller than the heat conducting section, thus contact area between them is very limited. Consequently, with the plate-type and the pin-type heatsinks, the heat dissipation fins as a whole often fail to function effectively.
It could be argued that if the amount of air flow around the heat dissipation fins is the same, the heat dissipating capacity can be increased by expanding the surface area by increasing the number of fins. In reality however, considering unit area, when the sectional area of the heat dissipation fins is increased, the area where air can flow into, such as an air flow area 7e (marked with diagonal lines in FIG. 15(a)) decreases, so does the total volume of air flow. Therefore, in some cases, the heat dissipation capacity lowers as a result. In other words, a mere increase in the number of dissipation fins does not bring about an improvement.
The most important aspect for the dissipation of heat is to effectively conduct heat produced by the heat producing element to the dissipation fins over the largest possible area. Considering this point, the tower-type heatsink shown in FIG. 16 has been introduced. In this kind of heatsink, heat produced in the heat producing element is conducted directly to the upper part of the heatsink by a central column, and spread flatly by the plate fins formed at a right angle to the axis of the column. The heat which has been spread flatly on the both faces of the thin plates is generally dissipated into the air by natural air cooling. In this tower-type heat sink, improvements have been proposed to increase the dissipation capacity. For example, Japanese Utility Model Application Unexamined Publication No. S62-182600 discloses a heatsink where through-hole vents are formed on the surface of the thin plates by cutting and folding the cut edges of the thin plates in the process of producing-the plate fins. Through these vents, air is permitted to convect more easily in the direction parallel to the axis of the column.
However, development of even faster electronic components such as semiconductors has resulted in a relative increase in the amount of heat produced. As a result, conventional cooling apparatus are now facing difficulties in cooling electronic components sufficiently, especially when it comes to electronic components such as MPU which produce significant amount of heat, the conventional cooling apparatus fail to reach their full capacity. In some cases, temperature rise in MPUs has led to thermal runaway and caused electronic apparatus to malfunction. To deal with increases in heat generation, it is possible to enhance the cooling capacity by making the cooling apparatus itself larger. However, the size of the electronic apparatus itself inevitably limits the size and weight of the cooling apparatus.
Compared with other types, the construction of the tower-type heatsink provides a better heat conductivity, however, it also tends to trap air. Furthermore, it is difficult to dispose a cooling fan on the top of the tower-type heatsink, therefore, the cooling fan must be disposed on a side face of the heatsink. However, if the cooling fan is disposed in such a manner, the heatsink is required to be as high as the width of the cooling fan. Thus, the cooling apparatus as a whole becomes remarkably large. Despite its size, however, the dissipation efficiency can not be improved satisfactorily.
The present invention aims to address the foregoing problems, and to provide a compact and highly efficient heatsink and a small cooling apparatus with high cooling ability using the heatsink. The present invention further aims at providing a method of manufacturing the heatsink which achieves the production of a highly effective heatsink in a productive and inexpensive manner.
A heatsink of the present invention has a column having a heat conducting plate with a heat receiving face in contact with a heat producing element. On the side faces of the column are a plurality of first slits disposed parallel to the heat receiving face and a plurality of second slits disposed transversely to the first slits. These slits form a plurality of pillar-type protrusions functioning as cooling fins. The first and the second slits on the side faces of the column are of different depth. Hereinafter, the pillar-type protrusions are called fins.
The sectional area of the column of the heatsink of the present invention tapers off toward both ends gradually or in stages from the vicinity of where the heat producing element is mounted.
The width of the second slits on the side of the column is wider at both ends than at the center of the heatsink or in the vicinity of the heat producing element.
The central line of the heat receiving face and that of the column are not aligned.
The heatsink of the present invention is compact, yet it has high heat dissipation properties and can effectively lead the heat produced by the heat producing element throughout the heatsink.
The manufacturing method of the heatsink of the present invention includes first and second processes. In the first process, the first slits are formed by providing a plurality of plate fins on the column and its longitudinal directions. Methods for providing the metallic plate include the extrusion molding using a metallic mold. In the second process, the second slits are formed in a direction approximately transverse to the longitudinal direction of the-plate fins. In other words, in the manufacturing method of the heatsink of the present invention, the pillar-type protrusions are produced by the two processes to form slits, and are used as cooling fins. The pillar-type protrusions are described as fins hereinafter.
This manufacturing method achieves productive and inexpensive production of high-performance heatsinks.
The cooling apparatus of the present invention includes a cooling means mounted on the heatsink of the present invention. As a wind blowing means such as a fan is mounted on the top face of the heatsink, the cooling apparatus of the present invention achieves a high cooling ability and a compact body.